The cytochrome P450 enzymes are important enzymes in the liver that trigger drug metabolismreactions. In biotechnology and biomimetic chemistry, synthetic models of the active species of P450 havebeen developed and designed and often react differently. Here, we investigate a biomimetic P450 modelcomplex with phthalocyanine equatorial ligand rather than heme or porphyrin and with and without four tert- butylsubstituents to the periphery of the ligand. Density functional theory studies on the electronic propertiesof the active species of the system, namely the iron(IV)-oxo with equatorial ligand cation radical species andits reactivity in oxygen atom transfer were studied. The work shows that a phthalocyanine equatorial ligandrather than porphyrin leads to a dramatic effect on the orbital energy levels of the iron(IV)-oxo species andcreates a species with close-lying doublet and quartet spin states with two unpaired electrons in π*xz and π*yzfor the Fe-O interaction coupled to a ligand radical in an a1u-type orbital. The latter contrasts P450 CompoundI that has the a1u orbital doubly occupied and a singly occupied a2u orbital instead, As a consequence,our biomimetic model gives a reduced redox potential as compared to a system with a porphyrin-basedradical and makes it a weaker oxidant. Nevertheless, the iron(IV)-oxo cation radical species with phthalocyanineligand is shown to react with para-X-substituted thioanisole (X = CH3, Cl, CN, H, NO2, OCH3)substrates with small oxygen atom transfer barriers that align with the σ-Hammett parameter. The reactionsare concerted with a single barrier leading to sulfoxide products.
Synopsis: A series of density functional theory studies are presented on the electronic properties of a phthalocyanine ligated iron(IV)-oxo cation radical species and its reactivity with para-substituted thioanisole substrates. The studies show that despite the fact the reactant is electronically different from cytochrome P450 Compound I, it should react with sulfides in a concerted synchronous manner efficiently.
Volume 133, 2021
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